I. Read and memorize the following words and expressions:

Branch of physical geography, to deal with , distribution, environment, to be affected by, mathematical terms, innumerable combinations, observational data, commonplace phenomena, to borrow, behaviour of water, to be apt, relationship, hydrologic cycle, essential constituent, to replenish, human body, density, to expand, pure water , saltness, total amount, invariable, economic activities, to meet needs, river estuary, medical treatment.

II. Read and translate:

Do you know , that :

a) … all the life on earth depends upon water ?

b) ... the total amount of water in existence equals 326 million cubic miles ?

c) ... about 97 per cent of that water may by found in the oceans ?

d) ... most of the rest is frozen in Antarctica and Greenland ?

e)… water covers 71 per cent of the earth's solid crust ?

f) ... hydrology in a broad and literal sense is the science of water, its properties,

phenomena and distribution ?

g) ... there are four general sources of water available to man: surface water , ground

water , atmospheric water and oceans ?

h) …water is put to a great variety of uses : for irrigating crops, for the generation of

hydroelectricity, for canals and waterways, for controlling pollution and as a

source of food ?

III. Select the right vocabulary definitions to the following words: air, Earth, water, sea,

nature, moisture, soil, ground, land:

1) Salt water which covers most of the Earth's surface. 2) The planet on which we live. 3) The system of which we ourselves are a part. 4) The mixture of gases that surrounds the Earth. 5) The common liquid which fills the rivers , lakes, seas and oceans. 6) Water vapour either in the air or condensed on a surface. 7) The earth in which things grow. 8) The surface of the Earth. 9) The solid part of the Earth's surface contrasted with water and sea.

Text A HYDROLOGY

Hydrology is a branch of physical geography which deals with the waters of the earth with special reference to their properties, phenomena and distribution. It is a science that treats of the waters of the earth, their occurrence, circulation and distribution, their chemical and physical properties, and their reaction with their environment, including their relation to living things. That is, the domain of hydrology embraces the history of water on the earth.

Although man has been greatly affected by water in the development of his civilization, and although there is an enormous literature on this subject, it is not yet possible to call hydrology an exact science because when given a factor such as rainfall, one cannot accurately deduce the resulting deposition of the water in scientific and mathematical terms. This inaccuracy is due to the great complexity of the hydrologic cycle, the lack of accurate observational data, and the almost innumerable combinations of hydrologic phenomena that occur in nature. Two phases of the water cycle  rainfall and runoff measured as stream flow - are such commonplace phenomena that many are apt to think that much is known about the behaviour of water. On the contrary , much is yet to be learned, for science is only now escaping from an almost complete dependence on relationship between these hydrologic factors. Hydrology provides the engineer with the basic data and methods required to solve problems relating to the regulation, control and utilization of water. Generally, five subdivisions of hydrology are recognized: 1) potomology  the study of surface streams. 2) limnology  the study of lakes, 3) cryology  studies dealing with snow and ice, 4) geohydrology  studies related to subsurface waters and 5) hydrometeorology  the study of problems intermediate between the fields of hydrology and meteorology. However, very few hydrologic problems can be limited to but one of these branches. It means that hydrology is an extremely broad science and therefore borrows from other branches of science and integrates them for its own interpretation and use. Such sciences as physics, mathematics, statistics, geology, geography, chemistry, computer science are but a few which may be used in hydrologic investigations.

Text В THE ROLE OF WATER IN NATURE

AND MAN'S LIFE

Water , the most essential constituent of the biosphere, may be found in nature in gaseous, liquid and solid state. Water is a powerful factor that remakes the earth's surface and is the only source of the process of replenishing oxygen in the atmosphere that is continuously going on in photosynthesis.

Water is one the commonest of all substances, and without it life would be impossible. The seas and oceans cover about seven-tenth of the Earth's surface but water is also contained in the soil, in the atmosphere and in all living things. More than half of the human body consists of water, which also form a large part of the food we eat, especially vegetables and fruits. Man cannot live as long as ninety days or more without water.

Water exists as a substance in three states : ice, which melts at 0 degrees Centigrade; liquid and steam, the latter is formed when water boils at 100 degrees Centigrade.

Water differs from other liquids in that it expands when cooled from 0^oC, contracts when heated from 0⁰C to 4°C, and reaches its maximum density at 4° C. No other liquid possesses this property.

Pure water is rarely found in nature. This is because water is able to dissolve so many substances from the air, the soil and the rocks. The saltness of sea water is caused by the mineral substances which are dissolved from the Earth's surface by rivers and carried down to the sea. The Sun's heat causes the surface sea water evaporate, or change into vapour, leaving behind the salt and other minerals. This explains why the seas are much more salty than rivers flowing into them.

The total amount of water contained in our planet is constant and invariable and can neither be increased, nor diminished.

Water is necessary for many aspects of man's life and economic activities. Great amounts of water, are daily used for agriculture needs for irrigation. Ever-growing amounts of water are used to meet industrial and domestic needs of the cities. Cascades of hydro-electric stations are going up on big rivers to generate tremendous amounts of electrical energy. Many water wells, lakes, rivers and seas estuaries are used for medical treatment.